Secretary of State Rex Tillerson in an op-ed for The New York Times on Wednesday defended President Donald Trump's handling of the situation with North Korea and said Americans should be "encouraged" by the United States' progress in dealing with "immense challenges" this year.

Tillerson, who has had a rocky first year under Trump, said the president identified North Korea as the United States' "greatest security threat" when he took office, and has taken many steps this year to isolate Pyongyang by carrying out a "policy of pressure through diplomatic and economic situations."

But he called on China to step up and "do more."

"A central component of our North Korea strategy is persuading China to exert its decisive economic leverage on Pyongyang," he said. "China has applied certain import bans and sanctions, but it could and should do more."

Tillerson also touted the administration's war on defeating terrorism, saying "the Global Coalition to Defeat ISIS has accelerated operations and has recaptured virtually all of previously held Islamic State territory in Iraq and Syria."

He also said Pakistan must contribute on that front.

"We are prepared to partner with Pakistan to defeat terrorist organizations seeking safe havens, but Pakistan must demonstrate its desire to partner with us."

Tillerson also said the U.S. is on guard against Russian aggression, but "we recognize the need to work with Russia where mutual interests intersect."